The invention relates to a semi-conductor module with an encapsulating mass that covers a semi-conductor.
U.S. Pat. No. 7,034,660 B2 discloses a wireless sensor that is embedded in concrete or any other cement-containing material in order to detect parameters that are indicative of changes in construction materials. The sensor can be, for example, an electrochemical sensor that is well-suited for detecting chloride ions.
Preferably, the encapsulation of individual semi-conductors and semi-conductor sub-assemblies (including passive components) on substrates is effected nowadays with organic masses based on epoxy resin, with, in some cases, organic filling materials, such as silicon dioxide (SiO2). U.S. Pat. No. 4,529,755, for example, discloses an encapsulating mass of this type comprising a poly-functional epoxy compound, a styrene-type block copolymer, a hardener for the epoxy compound, and an inorganic filler.
These encapsulated components and sub-assemblies typically have electrical connectors and cooling connection surfaces for the integrated power components. Hardened epoxy resins (non-reinforced) have typical thermal expansion coefficients (CTE, coefficient of thermal expansion) of approx. 60-80 ppm/K. Substrates (ceramic, metal, and organic core circuit boards) possess clearly lower thermal expansion coefficients (3-20 ppm/K). For applications of power electronics, the focus is on components and sub-assemblies with high power dissipation and, to some extent, high operating voltages as well, i.e., insulation requirements. It is customary in power electronic components and sub-assemblies to mainly use ceramic substrates with cores made of Al2O3, AlN or Si3N4 having CTEs of 3-8 ppm/K.
In this context, these sub-assemblies are further encapsulated by organic masses, which have to compensate for the mal-adaptation to the ceramic substrate due to elastic expansion and deformation of the module. However, this mal-adaptation between ceramic substrate and encapsulating mass and the ensuing mechanical shear stress lead to delamination and destruction of the inner contacting, e.g., bond wires.
Enriching the organic matrix material with fillers showing low expansion leads to low viscosities and critical behavior during processing. The masses become liquefied at high temperatures and are pressed into the cavities of the tool shells at high pressure in order to ensure that the filling is free of shrink holes. However, this process is error-prone proportional to the increasing degree of filling (shrink hole) and very energy-consuming due to the high temperatures (160° C.-200° C.) and pressures (15-25 MPa).
Finally, the need to have an organic matrix leads to the thermal conductivity being very low and usually being only insignificantly higher than the thermal conductivity of epoxy resins (approx. 0.4 W/mK), despite the admixture of filler contents.